Solenoids are often used as the driver to operate many types of electromechanical devices, such as for example electromechanical door latches or strikes. In the case of door latches, electromagnetic devices may also be used as drivers. In the use of solenoids as drivers in electromechanical door latches or strikes, the solenoids may be spring-biased to either a default locked or unlocked state, depending on the intended application of the strike or latch. When power is applied to the solenoid, the solenoid is powered away from the default state to bias a return spring. The solenoid will maintain the bias as long as power is supplied to the solenoid. Once power has been intentionally removed, or otherwise, such as through a power outage from the grid or as a result of a fire, the solenoid returns to its default locked or unlocked state.
In a fail-safe lock system, power is supplied to the solenoid to lock the latch or strike. With power removed, a return spring moves the mechanism to an unlocked state. Thus, as long as the latch or strike remains locked, power has to be supplied to the solenoid to maintain stored energy in the return spring.
The current to pull in the plunger of the solenoid is referred to as the “pick” current and the current to hold the plunger in its activated position is referred to as the “hold” current. Typically, the pick current is much greater than the hold current.
In a fail-secure system, the reverse is true. With power removed, the return spring moves the latching mechanism to a locked state. Thus, as long as the latch remains unlocked, power has to be supplied to the solenoid to maintain stored energy in the return spring. Again, the hold current is typically much less than the pick current.
A system designed to overcome the shortcomings of solenoid lock systems is disclosed in the prior art disclosure from Sargent Manufacturing Company (WO2014/028332—herein referred to as “the '332 publication”), the entirety of which is incorporated herein by reference. As disclosed in the '332 publication, the solenoid used to drive the door latch mechanism is replaced by a small DC motor that moves a latching plate. This change, in combination with the motor aligning with and engaging an auger/spring arrangement, reduced standby current consumption of the driver from about 0.5 A to about 15 mA.
U.S. Pat. No. 9,183,976, filed Mar. 15, 2013, and assigned to Hanchett Entry Systems, Inc. discloses a springless electromagnet actuator having a mode-selectable magnetic armature that may be used in door latching applications. A standard solenoid body and coils are combined with a non-magnetic armature tube containing a permanent magnet, preferably neodymium. The magnet is located in one of three positions within the armature. When biased toward the stop end of the solenoid, it may be configured to act as a push solenoid. When biased toward the collar end of the solenoid, it may be configured to act as a pull solenoid. In either case, no spring is required to return the armature to its de-energized position. Positioning the magnet in the middle of the armature defines a dual-latching solenoid requiring no power to hold it in a given state. In one aspect, a positive coil pulse moves the armature toward the stop end, whereas a negative coil pulse moves the armature toward the collar end. The armature will remain at the end to which it was directed until another pulse of opposite polarity is supplied to the actuator.
Irrespective of the type of electromagnetic actuator used, power to the inductive load of an electric latch or strike (such as a solenoid, DC motor, or magnetic actuator) is most efficiently maintained if a constant current is provided to the inductive load. Therefore, there exists a need for a constant-current controller operable to supply a constant current to the inductive load. The present invention fills this need and other needs.